Non-competitive NMDA receptor antagonists

ABSTRACT

Disclosed herein are non-competitive NMDA receptor antagonists having chemical structures similar to that of phencyclidine (PCP). These antagonists contain a polycyclic ring structure in place of the cycloalkyl ring of PCP. The antagonists also differ from PCP in that they include an electron withdrawing group, a hydroxyl group, or an amine group at the para position of the phenyl ring. The antagonists disclosed herein are useful for treating or ameliorating a symptom of ailments associated with over excitation of cells (e.g., neurons) that express NMDA receptors. Examples of ailments that can be treated and for which symptoms can be ameliorated include epilepsy, neurodegenerative disease (e.g., Alzheimer&#39;s and Parkinson&#39;s diseases), drug addiction, neuropathic pain, and neuronal and glutamate-dependent tumors.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is entitled to priority pursuant to 35 U.S.C. §119(e)to U.S. provisional patent application 60/805,164, filed on 19 Jun.2006.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This work was supported in part by grants from the National Institutesof Health (Grant Nos. 2R15NS3693-03A1 and 7R15N536393-04) and the U.S.Government may therefore have certain rights in this invention.

BACKGROUND OF THE INVENTION

The invention relates generally to the field of non-competitive NMDAreceptor antagonists that are analogs of phencyclidine (PCP). Thesecompounds contain a polycyclic ring structure in place of the cycloalkylring of PCP, as well as an electron withdrawing group, hydroxyl or aminogroup at the para position of the phenyl ring. The antagonists disclosedherein are useful for ameliorating, treating, and preventing ailmentsassociated with detrimental effects attributable to “over-activation” ofNMDA receptors on cells of various types, such as over-excitation ofneurons having NMDA receptors.

Neuronal damage, including brain damage, can occur via over-excitationof neurons. When over-excitation occurs, the membrane potentialcollapses and that can lead to cell death. The N-methyl-D-aspartate(NMDA) receptor appears to have a role in neurodegeneration that occursby means of this mechanism. When over-activated, the NMDA receptorallows excess calcium ions (i.e., Ca²⁺) to flow into the neuron bearingthe receptor, causing both necrosis and apoptosis of the neuron.

The NMDA receptor is a transmembrane protein located on neuronal cellsand has multiple ligand binding sites, including sites for glutamate,glycine, polyamine and cations (e.g., Zn²⁺ and Mg²⁺) and phencyclidine(PCP) binding as shown schematically in FIG. 1.

Rogawski reports that NMDA receptor channel blockers may act asneuroprotective agents. As illustrated in FIG. 1, PCP acts as anon-competitive antagonist of the NMDA receptor by binding in the ionchannel thereof and blocking the inflow of calcium ions into the neuron.However, PCP does not selectively interact with the NMDA receptor; PCPbinds with other neuronal receptors, including sigma (σ) receptors andcholinergic (nicotinic) receptors. PCP also inhibits uptake of biogenicamines (including dopamine, norepinephrine and epinephrine) andinteracts with voltage-gated potassium channels.

The multiple and various interactions and activities of PCP are thoughtto induce the well-known side effects of PCP ingestion, which includepsychosis and ataxia. These side effects and the high abuse potential ofPCP significantly limit the practical therapeutic value of thiscompound.

The psychotic and ataxic effects associated with PCP appear to bemediated by PCP binding to σ receptors. It has been recognized in theart that compounds that selectively bind to the PCP binding site of theNMDA receptor (relative to the PCP binding site of the σ receptor orother neuronal receptors) might be useful neuroprotective agents. Suchcompounds can act as selective, non-competitive antagonists of NMDAreceptor function. The literature proposes that development of PCPanalogs might provide useful therapeutic agents for treatment ofneurodegenerative conditions associated with over activation ofNMDA-bearing cells such as neurons in neurodegenerative conditions.However, data demonstrating the efficacy of any such analogs or types ofanalogs for this purpose have been lacking prior to this disclosure.

The present disclosure overcomes those shortcomings by providing NMDAreceptor antagonism data for compounds designed based onstructure-function analyses of PCP which were undertaken by the presentinvestigators in order to identify potentially efficacious therapeuticagents that inhibit NMDA receptor activity.

PCP has three moieties: a phenyl ring, a 6-membered cycloalkyl ring anda piperidine (cyclic amine) moiety, arranged as shown below:

Many PCP analogs are known and have been described. See, for example,Linders et al., 1993, J. Med. Chem. 36: 2499-2507; Thurkauf et al.,1990, J. Med. Chem. 33: 2211-2215; Johnson, 1985, Ann. Rep. Med. Chem.24, Chap. 5; Kamenka et al., 1982, J. Med. Chem. 25: 431-435; Kalir etal., 1969, J. Med. Chem. 12: 473-477; Cone et al., 1984, J. Pharmacol.Exp. Ther. 228: 147-153; Manallack et al., 1988, Mol. Pharmacol. 34:863-879; Bowen et al., 1993, Mol. Neuropharmacol. 3: 117-126; Quirion etal., 1992, Trends Pharmacol. Sci. 13: 85-86; Walker et al., 1990,Pharmacol. Rev. 42: 355-402; Rogawski, 1993, Trends Pharmacol. Sci. 14:325-331; Brennan, 1996, Chem. Eng. News 74: 41-45; de Costa et al.,1992, J. Med. Chem. 35: 4704-4712; Hays et al., 1993, J. Med. Chem. 36:654-670; Staley et al., 1996, Psychopharmacology, Berl., 127: 10-18;Keana et al., 1989, Proc. Natl. Acad. Sci. USA 86: 5631-5635; Reynoldset al., 1992, Eur. J. Pharmacol. 226: 53-58; Chen et al., 1992, J. Med.Chem. 35: 1634-1638; Rajdev et al., 1993, Br. J. Pharmacol. 109:107-112; Reynolds et al., 1990, Adv. Pharmacol. 21: 101-126; andOrtwine, 1994, ACS Satellite Television Seminar, “Molecular Modeling:The Small Molecule Approach,” pp. 47-65.

Adejare and Sun (The 228th ACS National Meeting, Philadelphia, Pa., Aug.22-26, 2004, Abstract MEDI 67) report the synthesis and chemicalcharacterization of two classes of fluorinated PCP analogs. In oneclass, the phenyl ring is replaced with a 2-fluorophenyl group, thecycloalkyl group with a bicycloalkyl group, and the amine is variously afree amine, pyrrolidine or piperidine. In the other class, the phenylmoiety is also replaced by a 2-fluorophenyl group and the amine isvariously a free amine, pyrrolidine or piperidine. However, in thisgroup, the cycloalkyl group is a cyclopentyl or cyclohexyl group.Although this report speculates that these PCP analogs might act asselective NMDA receptor antagonists, no suggestive or confirming data isprovided.

Sun and Adejare (AAPS PharmSci 5: Abstract M1127, October 2003) describesynthesis of nine PCP analogs, each having same bicycloalkyl group,namely a bicyclo[2.2.1]heptyl group. The remainder of the molecules havethe phenyl ring as a phenyl, 3-fluorophenyl or 4-fluorophenyl group withthe amine moiety being a free amine, pyrrolidine or piperidine. Thesenine PCP analogs are also speculated to potentially act as selectiveNMDA receptor antagonists, but again no suggestive or confirming data isprovided.

Without structure-function correlations, i.e., without pharmacologicalor biological data, the selectivity of PCP analogs for NMDA and σreceptors cannot be accurately predicted, nor can potential therapeuticefficacy of such analogs. For example, after assessing the biologicalactivity of some of the PCP analogs described by Adejare and Sun (2004)and Sun and Adejare (2003), it was subsequently discovered by thepresent investigators that many of the compounds disclosed in thosereferences are toxic and unsuitable for therapeutic use. The presentdisclosure is based, in part, on the unexpected finding that PCP analogshaving more constrained alkyl rings (i.e., those having multiple cyclicalkyl rings) and para-substituted phenyl rings exhibit suitable activityand have significantly less toxicity while exhibiting neuroprotectiveaction. As such, the present disclosure significantly advances theknowledge in this field.

BRIEF SUMMARY OF THE INVENTION

Disclosed herein are methods for using selective NMDA receptorantagonists to treat or ameliorate ailments associated withover-excitation of neurons and NMDA receptors. In certain embodiments,such methods comprise administering an antagonist to a subject for atime and in an amount sufficient to inhibit activity of an NMDAreceptor. Such inhibition can occur, for example, by blocking the ionchannel and preventing calcium influx into the cell. The methodsdescribed herein include use of antagonists having one of at least threegeneral chemical formulas.

Certain of the antagonists suitable for use in the methods disclosedherein contain a bicyclo[2.2.1]heptyl ring and are represented by theformula referred to herein as Structure A

Other antagonists suitable for use in the methods disclosed hereincontain a bicyclo[2.2.2]octyl ring and are represented by the formulareferred to herein as Structure B

Still other antagonists suitable for use in the methods disclosed hereincontain an adamantane moiety (multiple six-membered alkyl rings) and arerepresented by the formula referred to herein as Structure C

In each of Structures A, B, and C, the R moiety can be an electronwithdrawing group, hydroxyl group or an amino group. For example, R canbe a halo moiety such as a fluorine atom, a nitrate moiety, or ahalomethyl moiety such as a fluoromethyl group. In these threestructures, the cycloalkyl ring can have one or more of the poly-cyclicring hydrogen atoms independently substituted with a lower alkyl group,such as a methyl or ethyl group. Use of pharmaceutically acceptablesalts of these compounds is expressly contemplated.

When R is an electron withdrawing group, R can be a halo moiety (i.e., afluoro, chloro, bromo, or iodo atom), a nitrate moiety, or a halomethylgroup, such as a fluoromethyl group (including mono-, di-, andtri-fluoromethyl groups), for example. When the cyclic ring is abicyclo[2.2.1]heptyl ring (i.e., Structure A) and R is a fluoro group,then the compound is1-(2-(4-fluorophenyl)bicyclo[2.2.1]hept-2-yl)piperidine, also referredto herein as “bicyclo,4-F-PCP.”

The antagonists and methods disclosed herein are useful for treating,ameliorating, and preventing conditions associated with“over-activation” of NMDA receptors on cells of various types, such asneurons and glutamate-dependent tumor cells. Such conditions are knownin the art to include cerebral ischemia, stroke, brain trauma, braintumors, Alzheimer's disease, Parkinson's disease, epilepsy and otherconvulsive disorders, schizophrenia, acute and chronic neuropathic pain,sleep disorders, drug addiction (e.g., addiction to morphine and otheropiates), the psychological aspects of depression, vision disorders(e.g., retinal disorders such as macular degeneration), ethanolwithdrawal, anxiety, memory dysfunction, learning disabilities, andneurofibromatoses (e.g., neurofibromatosis type 1 {a.k.a. NF1} andmemory- and learning-deficiencies associated therewith).

By way of example, the compositions and methods described herein can beused to treat, ameliorate, or prevent convulsions or other symptomsassociated with epilepsy in a subject. This is achieved by administeringto the subject an NMDA receptor antagonist disclosed herein for a timeand in an amount sufficient to inhibit or reduce the symptom. Forexample, the subject can be treated with bicyclo,4-F-PCP. By way offurther example, the antagonists described herein can be used to treat,ameliorate, slow, arrest, or prevent neurodegenerative disorders, suchas Alzheimer's disease and Parkinson's disease. Such use entailsdelivering one or more of the antagonists to the affected or at-riskcells of a subject afflicted with, suspected of being afflicted with, orat risk for developing the disorder. Such delivery can be achieved byany of a variety of routes, such as oral administration of a solid orliquid composition including the antagonist, by injection of acomposition including the antagonist, or by local implantation of asustained-release composition including the antagonist.

The invention also includes the NMDA receptor antagonists describedherein and pharmaceutical formulations containing those antagonists. Inaccordance with U.S. and other national laws pertaining to packaging,sale, and use of pharmaceutically active agents, the compositionsdescribed herein can be formulated, packaged, and labeled for use inprevention, amelioration, or treatment of the conditions describedherein.

BRIEF SUMMARY OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a current model of the NMDA receptor, as described byWatkins et al., 1993, in “The NMDA Receptors”, Oxford University Press,Oxford, pp. 9 to 233.

FIG. 2 illustrates a scheme for synthesizing certain of the NMDAreceptor antagonists disclosed herein.

FIG. 3 illustrates the ability of bicyclo,4-F-PCP to compete with MK-801(dizocilpine) for binding to the NMDA receptor. In the figure, datacorresponding to the maleate salt of MK-801 are shown as open circles,and data corresponding to bicyclo,4-F-PCP (designated “063368-1” in thefigure) are shown as closed squares. The vertical axis representsspecific binding percentage, and the horizontal axis represents molarconcentration of the respective compound.

FIG. 4 illustrates non-competition of bicyclo,4-F-PCP with the NMDAreceptor competitive antagonist CGP 39653 for binding with the NMDAreceptor. In the figure, data corresponding to CGP 39653 are shown asopen circles, and data corresponding to bicyclo,4-F-PCP (designated“063368-1” in the figure) are shown as closed squares. The vertical axisrepresents specific binding percentage, and the horizontal axisrepresents molar concentration of the respective compound.

DETAILED DESCRIPTION OF THE INVENTION

General Description and Definitions

Disclosed herein are selective NMDA receptor antagonists and methods forusing the antagonists to treat, ameliorate, or prevent conditions and/orailments associated with over-activation of NMDA receptors. Such methodsinvolve administering an NMDA receptor antagonist of the type describedherein, or a pharmaceutically-acceptable salt thereof, to a subject fora time and in an amount sufficient to inhibit activity of that receptorand/or reduce a physiological consequence of activation of the receptor,such as neuronal stimulation resulting from activation of NMDA receptorson neurons. The antagonists disclosed herein are represented by thechemical formulas shown in Structures A, B, and C.

Structures A, B, and C are

In each of Structures A, B, and C, the R moiety is an electronwithdrawing group, a hydroxyl group or an amino group. The cycloalkylrings of any of Structures A, B, and C (i.e., the bicyclo[2.2.1]heptylrings of Structure A, the bicyclo[2.2.2]octyl rings of Structure B, andthe rings of the adamantane moiety of Structure C) can have a loweralkyl group, such as a methyl or ethyl moiety independently substitutedin place of one or more of the ring hydrogen atoms.

The term “electron-withdrawing group” is known in the art and denotesthe tendency of a substituent to attract valence electrons fromneighboring atoms, i.e., the substituent is electronegative with respectto neighboring atoms. Examples of electron-withdrawing groups includenitro, acyl, formyl, alkylsulfonyl, arylsulfonyl, trifluoromethyl,cyano, halo (e.g., fluoro, chloro, bromo, and iodo) moieties, and otherelectron-withdrawing groups are known. In embodiments described herein,halo, nitrate and fluoromethyl groups (CF₃, CHF₂ or CH₂F) are disclosedas suitable electron withdrawing groups.

Instead of being an electron withdrawing group, R can instead be ahydroxyl or an amino group. In certain embodiments, hydroxyl or amino Rgroups are included both for therapeutic efficacy, and because they canprovide reactive intermediates for the synthesis of compounds describedherein that include electron withdrawing groups as the R moiety. Forexample, compounds wherein R is an amino group can be converted tocompounds wherein R is an acetamide group.

As used herein, “lower alkyl” means branched- and straight-chain,saturated aliphatic hydrocarbon groups having from 1 to 6 carbon atoms.Lower alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, tert-butyl, all pentyl isomers and all hexyl isomers. Suitablelower alkyl groups include methyl and ethyl groups.

Synthesis of Antagonists and Their Pharmaceutically-Acceptable Salts

The antagonists disclosed herein can be synthesized by the generalscheme shown in FIG. 2 or by adaptation thereof. For example, a Grignardreaction can be used to react the appropriate polycyclic ring ketoneprecursor with a 1-bromo-4-substituted benzene (e.g.,1-bromo-4-fluorobenzene or 1-bromo-4-trifluoromethylbenzene) to producetertiary alcohols corresponding to compound III of FIG. 2. Thosealcohols are converted to the corresponding amines (compound IV of FIG.2) by reaction with sodium azide followed by reduction with lithiumaluminum hydride (LAH). The amines are reacted with 1,5-dibromopentaneto produce the corresponding piperidine analogs. The amine hydrochloridesalts can be prepared by bubbling hydrogen chloride through the ethylether solutions (or other appropriate solvents) of the amines.

Methods for purification and characterization of the antagonists, suchas crystallization or preparative chromatography, are also well known tothose of skill in the art. For example, the crude mixtures can bepurified by preparative thin layer chromatography (TLC) with a mobilephase composed of chloroform and ethyl ether (9:1). Desirable solventsfor crystallization include chloroform and hexane, but appropriatesolvents can be readily determined by those of skill in the art.

Pharmaceutically-acceptable salts of the antagonists can be prepared byreacting the free acid or base forms of these compounds with astoichiometric or greater amount of the appropriate base or acid inwater or in an organic solvent, or in a mixture of the two; generally,non-aqueous media like ether, ethyl acetate, ethanol, isopropanol, oracetonitrile are particularly well-suited. These salts can also beprepared by ion exchange.

Pharmaceutical Formulations

An antagonist disclosed herein can be made or formulated as apharmaceutically-acceptable salt. “Pharmaceutically-acceptable” saltsare well known in the art and refer to derivatives of the disclosedcompounds that include acid or base cations or salts. Examples includemineral or organic acid salts of the basic residue of the piperidinemoiety or of any basic residue on the substituted phenyl ring (e.g., theamine moiety of an antagonist wherein R is an amine group). Otherexamples include alkali or organic salts of acidic residues on thephenyl ring.

Pharmaceutically-acceptable salts can include sulfate, pyrosulfate,bisulfate, sulfite, bisulfite, phosphate, ammonium, monohydrogenphosphate, dihydrogen phosphate, metaphosphate, pyrophosphate, chloride,bromide, iodide, acetate, propionate, decanoate, caprylate, acrylate,formate, isobutyrate, caprate, heptanoate, propiolate, oxalate,malonate, succinate, suberate, sebacate, furmarate, hippurate, maleate,butyne-1,4-dioate, hexyne-1,6-dioate, benzoate, chlorobenzoate,methylbenzoate, dinitrobenzoate, hydroxylbenzoate, methoxybenzoate,phthalate, sulfonate, xylenesulfonate, phenylacetate, phenylpropionate,phenylbutyrate, citrate, lactate, α-hydroxybutyrate, glycolate, maleate,tartrate, methanesulfonate, propanesulfonate, naphthalene-1-sulfonate,napthalene-2-sulfonate, mandelate, magnesium, tetramethylammonium,potassium, trimethylammonium, sodium, methylammonium, calcium, and likesalts. Lists of suitable salts are found in, for example, Remington,2006, The Science and Practice of Pharmacy, 21 st Edition, LippincottWilliams & Wilkins.

An antagonist disclosed herein can exist as a single stereoisomer, or asa mixture of stereoisomers. For example, the antagonist can be made andused in the form of an enantiomer or as a racemic mixture ofenantiomers. Similarly, pure and mixed diastereomers can be made andused. The pharmaceutical compositions described herein can include anindividual (i.e., substantially purified) stereoisomer, mixtures ofstereoisomers, and racemic mixtures thereof. Methods of screeningstereoisomers for toxicity and efficacy are described herein and areotherwise well known in the art. In view of the known stereoselectivityof many cell-surface receptors, it is foreseeable that NMDA receptorswill exhibit binding preference (i.e., lower K_(i) value) for onestereoisomer of each antagonist described herein, relative to anotherstereoisomer. Although the preferred stereoisomer is not immediatelypredictable a fortiori, comparison of binding (and antagonism) abilityof stereoisomers is routine in the art and can be performed using theassays described herein or as otherwise known in the art.

An antagonist disclosed herein can be formulated as a pharmaceuticalcomposition comprising one or more of the antagonists described hereintogether with a pharmaceutically-acceptable carrier. Suitablepharmaceutical carriers are described, for example, in Remington TheScience and Practice of Pharmacy, 21st Edition (Lippincott Williams &Wilkins, 2006). Pharmaceutically-acceptable carriers can be sterileliquids, such as water and oils, including those of petroleum, animal,vegetable or synthetic origin, such as peanut oil, soybean oil, mineraloil, and sesame oil. In particular embodiments, water is an advantageouscarrier, such as when the pharmaceutical composition is administeredintravenously. Likewise, saline solutions, aqueous dextrose, andglycerol solutions are similarly advantageous in certain embodiments,particularly for injectable solutions. If a particular antagonistexhibits relatively low solubility in aqueous systems, any of a widevariety of alternative pharmaceutically acceptable solvents andadditives are known that can improve the solubility of the antagonist inthe vehicle desired for delivery. By way of example, the antagonist canbe dissolved and/or suspended in an alcohol (e.g., ethanol) solution orin a composition including DMSO or a detergent.

In addition to the pharmacologically active agent, the pharmaceuticalcompositions described herein can include suitablepharmaceutically-acceptable carriers, such as those comprisingexcipients and auxiliaries to facilitate processing of the activecompounds into formulations for delivery to the site of action. Suitableformulations for parenteral administration include aqueous solutions ofthe active compounds in water-soluble form; for example, water-solublesalts. Oily injection suspensions of the active compounds may also beadministered. Suitable lipophilic solvents or vehicles include fattyoils, such as sesame oil or synthetic fatty acid esters (e.g., ethyloleate or triglycerides). Aqueous injection suspensions can containsubstances that increase the viscosity of the suspension. These include,for example, sodium carboxymethyl cellulose, sorbitol, and dextran.Optionally, the suspension can also contain stabilizers. Thecompositions can also include solubilizing agents (e.g., cyclodextrins)for improving the amount of the antagonist(s) dissolved (i.e., ratherthan suspended) in a liquid component of the composition. Liposomes canalso be used to encapsulate the agent for delivery into the cell, andcan improve delivery of an antagonist described herein across theblood-brain barrier. Improved delivery of an antagonist across theblood-brain barrier can also be achieved by administering a compositionincluding the antagonist having a very small (e.g., micronized) form ofthe compound.

The pharmaceutical formulation for systemic administration as disclosedherein can be formulated for enteral, parenteral or topicaladministration. Indeed, all three types of formulations can be usedsimultaneously to achieve systemic administration of the activeingredient.

Suitable formulations for oral administration include hard or softgelatin capsules, pills, tablets, including coated tablets, elixirs,suspensions, syrups or inhalations and controlled release forms thereof.

The antagonists described herein can also be incorporated intopharmaceutical compositions which allow for sustained delivery of thosecompounds to a mammal for a period of several days, several weeks, or amonth or more. Such formulations are described, for example, in U.S.Pat. Nos. 5,968,895 and 6,180,608 and are otherwise known in the art.Any pharmaceutically-acceptable, sustained-release formulation known inthe art is contemplated.

For topical administration, any common topical formulation such as asolution, suspension, gel, ointment, salve, or similar composition canbe employed. Preparations of such topical formulations are described inthe art of pharmaceutical formulations as exemplified, for example, byRemington, 2006, The Science and Practice of Pharmacy, 21 st Edition,Lippincott Williams & Wilkins. For topical application, the antagonistsas disclosed herein can be administered as a powder or spray,particularly in aerosol form, for example.

The active ingredient can also be administered in pharmaceuticalcompositions adapted for systemic administration. If a drug is to beadministered systemically, it can be confected as a powder, pill, tabletor other solid composition or as a syrup, elixir or other liquidcomposition for oral administration. For intravenous, intraperitoneal orintra-lesional administration, the active ingredient is prepared as asolution or suspension capable of being administered by injection. Incertain cases, it may be useful to formulate the active ingredient insuppository form or as an extended release formulation for deposit underthe skin or intramuscular injection.

The antagonists described herein can be administered by inhalation. Forinhalation therapy, the compound can be in a solution useful foradministration by metered dose inhalers or in a form suitable for a drypowder inhaler, for example.

Pharmaceutical compositions expressly include both those formulated andintended for ethical administration to humans and veterinarycompositions formulated and intended for administration to non-humananimals.

Therapeutic, Preventative, and Ameliorative Applications

Described herein are methods of treating, ameliorating, preventing, orsome combination of these, conditions associated with over activation ofNMDA receptors. “Over-activation” of NMDA receptors on a cell meansoccurrence of one or more physiological consequences of NMDA receptorbinding with glutamate (or aspartate) to an extent or degree that apathological condition results. By way of example, many neurologicaldisorders (including neurodegenerative disorders such as Alzheimer's andParkinson's diseases) are attributable to over activation of cellsbearing NMDA receptors. Likewise, it is known that certainglutamate-dependent tumors rely on NMDA receptor activation for theircontinued survival.

These methods involve administering one or more NMDA receptorantagonists of the type described herein (or a pharmaceuticalcomposition including such an antagonist) to a subject afflicted withsuch a condition. The antagonist(s) are administered for a duration oftime and in an amount sufficient to inhibit activity of the receptor andto thereby reduce, prevent, or eliminate the corresponding pathologicalcondition or a symptom of that condition. The antagonists used in thesemethods are those PCP analogs described herein—i.e., those havingconstrained cycloalkyl rings (i.e., having polycyclic alkyl rings), apara-substituted phenyl ring, and a piperidine moiety. Such compoundsare represented by Structures A, B, and C, as described herein.Bicyclo,4-F-PCP is an example of an antagonist suitable for use in thesemethods.

It is contemplated that the antagonists described herein can beadministered in the form of one or more prodrugs which, uponadministration to a subject, are metabolized or otherwise acted upon bythe normal (or pathological) biochemical processes of the subject's bodyto yield an antagonist described herein. By way of example, an ester oramide of an antagonist described herein can be administered to asubject, the ester or carboxylic acid group thereof being removed in thesubject's body, yielding the active antagonist. Design and synthesis ofactivatable prodrugs is routine and within the ken of the skilledartisan in this field, and the methods described herein foradministering the antagonists described herein include administration ofcorresponding prodrugs.

The antagonists disclosed herein are capable of interacting with orbinding with the NMDA receptor (presumably at or near the PCP bindingsite of the receptor) to significantly reduce or prevent influx ofcations, especially calcium cations, mediated by the receptor. Bindingactivity can be assessed in vitro, if needed, by assay techniques knownto those of skill in the art. Likewise, calcium and cation flux assaysin neuronal cells are well known, see, e.g., Rogers et al. (1995)Biophys. J. 68:501-506. In the methods described herein, one or moreantagonists is administered to a subject afflicted with, believed to beafflicted with, or at risk for affliction with a disorder describedherein. The antagonist is administered in an effective amount, such aneffective amount being an amount sufficient to alleviate, eliminate, orprevent at least one symptom of the disorder. An effective amount canalso be viewed as the amount of antagonist that reduces, eliminates, orprevents a physiological consequence of activation of the receptor, suchas neuronal over-stimulation resulting from over-activation of NMDAreceptors on neurons.

The neurological conditions treatable in accordance with antagonists andmethods disclosed herein are those that are associated withover-excitation of neurons and/or the NMDA receptor. These conditionsinclude cerebral ischemia, stroke, brain trauma, brain tumors,Alzheimer's disease, Parkinson's disease, epilepsy, schizophrenia, acuteneuropathic pain, chronic neuropathic pain, sleep disorders, drugaddiction, depression, certain vision disorders, ethanol withdrawal,anxiety, and memory and learning disabilities. When measured in rat andmouse models, the antagonists disclosed herein exhibit anti-convulsiveactivity and this demonstrates that compositions including suchantagonists are suitable for treating epilepsy and other conditionsassociated with convulsions. This also demonstrates that oraladministration of such antagonists results in delivery to brain tissue(i.e., across digestive and blood-brain barriers) of an amount ofantagonist sufficient to treat, alleviate, or prevent chronic conditionssuch as neurodegenerative disorders, in that the amount of antagonistrequired for alleviation of acute conditions such as convulsions isexpected by a skilled artisan to be much (e.g., about 2-fold to 10-foldor more) higher than the amount necessary for chronic conditions.

In one embodiment, the methods described herein are used to treat orameliorate convulsions or other epileptic activity in a subjectexperiencing (immediately or intermittently) such activity. Such methodsinvolve administering a composition including one or more of the NMDAreceptor antagonists described herein to the subject for a time and inan amount sufficient to inhibit or reduce the convulsions or activity.Bicyclo,4-F-PCP is a suitable compound for use in this embodiment.

Tumors can be treated, or their symptoms ameliorated, using the NMDAreceptor antagonists disclosed herein. Rzeski reported colonadenocarcinoma, astrocytoma, and breast and lung carcinoma cells aresensitive to the anti-proliferative effect of the NMDA antagonistdizocilpine. Rzeski also reported that breast and lung carcinoma, colonadenocarcinoma, and neuroblastoma cells responded favorably to theamino-3-hydroxyl-5-methyl-4-isoxazole-propionate antagonist (AMPA)GYK152466. Rzeski et al., 2001, Proc. Natl. Acad. Sci. USA 98:6372-6377.Cavalheiro reported that the NMDA antagonist dizocilpine (MK-801) andthe AMPA antagonist GYK152466 limit proliferation of cancer cells in awide variety of human non-neuronal cancers, including not only colon,breast, lung, and thyroid carcinoma, but also glial and neuronal tumors,such as astrocytoma, neuroblastoma, andmedulloblastoma/rhabdomyosarcoma. Cavalheiro et al., 2001, Proc. Natl.Acad. Sci. USA 98:5947-5948. According to both research groups, theanti-proliferative effect was attributable to decreased cell divisionand increased cell death. Further, both groups reported that theanti-proliferative effect of glutamate antagonists is calcium dependent,which is consistent with the known calcium permeability of glutamatereceptor/ion channel complexes. Several other NMDA and AMPA receptorantagonists exhibit anti-cancer activity, evidencing involvement of NMDAand AMPA receptors in these tumors.

The compositions described herein are useful in methods of treatingglutamate-dependent tumors, ameliorating the symptoms of such tumors, orboth. Such methods involve administering a composition including one ormore NMDA receptor antagonists of the type described herein to a subjecthaving such a tumor. The composition including the antagonist isadministered for a time and in an amount sufficient to ameliorate one ormore symptoms associated with the glutamate-dependent tumor. Suchsymptoms include, for example, convulsions associated with or occurringbecause of the presence of brain tumors. Any measurable change in thetumor, such as shrinkage, or changes in cognitive or motor abilities(for neuronal tumors, including brain tumors) can be monitored to assessefficacy. Additionally or alternatively, methods of treatingglutamate-dependent tumors independently include administering theantagonists for a time and in an amount to relieve pain associated withthose tumors. Pain relief is thus another measure of efficacy of theantagonists.

Examples of glutamate-dependent tumors include non-neuronal tumors suchas colon adenocarcinoma, breast, lung, and thyroid tumors. Glial andneuronal tumors, such as astrocytoma, neuroblastoma, andmedulloblastoma/rhabdomyosarcoma are also examples ofglutamate-dependent tumors.

One way to measure the anti-cancer (or anti-tumor) effect of the NMDAreceptor antagonists disclosed herein is to observe morphologicalalterations in tumor cells. Such alterations may include reducedmembrane ruffling and pseudopodial protrusions. Likewise, decreasedmotility and decreased invasive growth of tumor cells can be monitored.Since convulsions are often associated with symptoms of brain tumors,assessing the level and frequency of convulsions provides anothermeasure of efficacy that can be monitored. Assessment of themorphological, motility-inhibiting, and growth-inhibiting activities ofthe antagonists described herein can be performed using either or bothof in vitro and in vivo model systems known in the art, and suchassessments are within the ken of the ordinarily-skilled artisan in thisfield.

The antagonists disclosed herein (as well as theirpharmaceutically-acceptable salts and compositions including the same)can be administered to a wide variety of subjects. As used herein,subjects expressly include humans, laboratory animals (e.g., mice, rats,non-human primates, rabbits, and pigs), and domesticated or farm animals(e.g., cats, dogs, cattle, horses, swine, sheep, goats, fish, lizards,and chickens and other birds).

As used herein, the term “administering” includes dispensing,delivering, or otherwise applying a compound disclosed herein in amethod disclosed herein, e.g., in a pharmaceutical formulation, to asubject by any suitable route for delivery of that compound to thedesired location in the subject. Expressly contemplated approachesinclude delivery by either the parenteral or oral route, intramuscularinjection, subcutaneous/intradermal injection, intravenous injection,buccal administration, transdermal delivery and administration by therectal, colonic, vaginal, intranasal or respiratory tract route (e.g.,by inhalation).

It is contemplated that the compounds disclosed herein are administeredin an effective amount, that being an amount sufficient to achieve adesired result, e.g., sufficient to inhibit activity of NMDA receptorsfor cells bearing such receptors (e.g., to reduce neuronal stimulationof NMDA receptor-bearing neurons). Reduction of neuronal stimulation canbe assessed directly (e.g., by assessing neuronal cells in vitro) or byassessment of a symptom (e.g., frequency, duration, or severity ofconvulsions) or other characteristic (e.g., memory retention) ofneuronal stimulation. An therapeutically beneficial amount of anantagonist described herein is an amount for which any toxic ordetrimental effects associated with administration of the amount of thecompound are outweighed by the therapeutically beneficial effectsassociated with such administration. For example, for the treatment ofepilepsy, a therapeutically beneficial amount is an amount that inhibitsor reduces convulsions (e.g., frequency, duration, or severity of suchconvulsions) or other symptoms associated with epilepsy (such asfrequency, duration, or severity of petit mal seizures). For treatmentof tumors, a therapeutically beneficial amount is an amount that leadsto improvement of a tumor characteristic in the subject, and such tumorcharacteristics include reduction of tumor size, lessening of frequencyor duration of tumor-related convulsions, prolonged survival,improvement in cognitive or motor abilities, reduction oftumor-associated pain, or any other measure available to assess tumorstatus in the subject.

Effective amounts of the compounds used in the methods described hereincan vary according to factors such as the disease state, age, and weightof the subject, and the ability of the compound to elicit a desiredresponse in the subject. Dosage regimens can be adjusted to provide theoptimum therapeutic response.

Suitable dosages for the compounds and methods disclosed herein rangefrom about 0.05, 0.1, 0.2 or 0.5 mg/kg body weight to about 100 or 200mg/kg body weight. In certain embodiments, dosages range from about 0.5to 1 mg/kg body weight to about 100 mg/kg body weight. In otherembodiments doses range from about 10 to about 50 mg/kg body weight.Performance of studies to determine an optimal dosage for a particularcondition using a particular compound is well within the level ofordinary skill in this field. The ED₅₀, for example, of bicyclo,4-F-PCPin rats for amelioration of electrically-induced convulsions is 28 mg/kg(milligrams of compound per kilogram of subject body weight), asdescribed herein in Example 2. As would be understood by a skilledartisan in this field, it is reasonable to expect that the ED₅₀ of anantagonist described herein would be significantly (e.g., about 2-foldto 10-fold or more) lower for alleviation, treatment, or prevention of achronic condition, such as neurodegeneration associated with Alzheimer'sdisease or Parkinson's disease than for chronic conditions (whichrequire much more of the antagonist) such as convulsions. For example,the ED₅₀ of bicyclo,4-F-PCP for alleviation, treatment, or prevention ofAlzheimer's and Parkinson's disease would be expected to be on the orderof 3 mg/kg.

EXAMPLES

The invention is now described with reference to the following Examples.These Examples are provided for the purpose of illustration only, andthe invention is not limited to these Examples, but rather encompassesall variations which are evident as a result of the teaching providedherein.

Example 1 Synthesis of PCP Analogs

The following materials were used to synthesize the antagonistsdisclosed herein: norcamphor (Lancaster), 4-bromofluorobenzene (99%),lithium aluminum hydride (LAH), ammonium hydroxide (28-30%), diethylether, hydrochloric acid (37.4%), H₂SO₄, sodium chloride, chloroform,N,N-dimethylformamide (99.9%), sodium azide (99%), 1,4-dibromobutane(97%), 1,4-dibromopentane, chloroform-d, THF (Fisher), and magnesiumturnings. THF was distilled over sodium, and injected by syringe under adry nitrogen atmosphere.

Instrumentation and Methods

Melting points were determined on a MEL-TEMP II capillary melting pointapparatus. MS spectra were collected with electrospray method using aFINNIGAN TSQ-700 mass spectrometer. NMR spectra were obtained on aVARIAN 300/54 300 MHz spectrometer. ¹H and ¹³C NMR spectra were recordedin CDCl₃ and respectively referred to internal TMS (0 ppm) and CDCl₃ (77ppm) signals. ¹⁹F-NMR spectra were obtained in CDCl₃ using CFCl₃ asinternal standard (0 ppm). All reported values are δ values in ppm.Column chromatographic separations were performed over ACROS gel No.7631-86-9, particle size 35-70 μm. Preparative thin layer chromatography(TLC) separations were performed on ANALTECH UNIPLATE silica gel GF 20cm×20 cm preparative TLC plates.

The compounds shown in Table 1 were synthesized according to the generalreaction scheme shown in FIG. 2. Briefly, norcamphor (compound II inFIG. 2) was reacted with a Grignard reagent of 1-bromobenzene,1-bromo-3-fluorobenzene or 1-bromo-4-fluorobenzene (compound I in FIG.2) to produce the corresponding2-(fluoro-phenyl)-bicyclo[2.2.1]heptan-2-ols (compound III in FIG. 2).These alcohols were converted to the corresponding amines using sodiumazide and LAH to produce compounds 1, 2 and 3 listed on Table 1(compound IV in FIG. 2). The crude amines were reacted with1,4-dibromobutane or 1,5-dibromopentane to produce the correspondingpyrrolidine analogs (compounds 5, 7 and 9; Table 1) or piperidinesynthesis (compounds 4, 6 and 8; Table 1), respectively (compound V inFIG. 2). The detailed synthesis and characterization of compounds 2 and4 is provided below. TABLE 1 Compound V Substituents (See Figure 2) Com-Com- pound R₁ R₂ pound R₁ R₂ 1 3′-F NH₂ 6 3′-F

2 4′-F NH₂ 7 3′-F

3 H NH₂ 8 H

4 4′-F

9 H

5 4′-F

Synthesis of (±)2-(4-fluorophenyl)-bicyclo[2.2.1]heptan-2-ol (III)

A mixture of 1-bromo-4-fluorobenzene (5.00 ml, 45.5 mmol), magnesiumturnings (3.32 g, 137 mmol), and a few iodine crystals in 70 ml dry THFwere vigorously stirred for 4 hours under the protection of nitrogen andcooling with ice/water. Norcamphor (5.00 g, 45.5 mmol) dissolved in 10ml dry THF was added drop-wise, and the reaction was allowed to warm upto room temperature and stirred overnight. The reaction was carefullyquenched with water and decanted from the excess magnesium turnings. Thereaction mixture in THF and water was adjusted to pH 7 with 2N HClsolution and extracted with chloroform (3×50 ml). The extract was driedover anhydrous sodium sulfate and the solvent was removed by vacuumevaporator. This resulted in an alcohol intermediate (III) appearing asa faintly yellow oil (9.4 g, 99%).

Synthesis of (±)2-(4-fluorophenyl)-bicyclo[2.2.1]hept-2-ylamine (2)

The alcohol intermediate III (9.4 g, 46 mmol) was dissolved in drychloroform (100 ml), and the flask soaked in ice/water. Sodium azide(8.89 g, 137 mmol) was added to the mixture, followed by trifluoroaceticacid (30.5 ml, 410 mmol) added in a drop-wise manner over a 20 minuteperiod. The mixture was stirred overnight, warmed to room temperature,and quenched with water and 80 ml saturated Na₂CO₃. The reaction mixturewas extracted with CHCl₃ (3×80 ml), dried over anhydrous sodium sulfateand evaporated. This resulted in a crude tertiary azide appearing as apale yellow oil (10.5 g).

The azide (10.5 g, 45.4 mmol) was dissolved in 20 ml dry THF, and thenadded drop-wise over a 30 minute period to a solution of lithiumaluminum hydride (2.60 g, 68 mmol) in 40 ml dry THF while the mixturewas cooled in ice/water. The reaction was quenched with ice after 10hours, and the slurry was vacuum filtered. The mixture was extractedwith diethyl ether (3×40 ml). Then, the mixture was further extractedwith 2N HCl solution (2×30 ml), and the ethereal solution discarded. Theacidic solution was adjusted to pH 9 with saturated ammonia solutionbefore it was again extracted by diethyl ether (3×40 ml). The ethereallayer was dried over anhydrous sodium sulfate and evaporated. Thisresulted in 2-(4 fluorophenyl)-bicyclo[2.2.1]heptan-2-amine (compound 2;Table 1), which appeared as a clear oil (6.6 g, 69%). This oil (0.4 g)was purified by preparative TLC using a mixture of chloroform anddiethyl ether (9:1, v/v) as mobile phase.

An off-white oil resulted from the purification, and after cooling offand crystallizing, the compound was characterized as follows by ¹H NMR(CDCl₃): δ 7.2 (m, 2H, 3′ and 5′ Ar—H); 6.8 (m, 2H, 2′ and 4′ Ar—H);1.0-2.6 (b, 10H, 4CH₂ and 2CH); ¹³C NMR (CDCl₃): δ 163.0 (s, 1C, 4′-C);160.4 (s, 1C, 1′-C); 128.6 (s, 1C, 5′-C); 128.5 (s, 1C, 3′-C); 115.3 (s,1C, 6′-C); 115.0 (s, 1C, 2′-C); 63.6 (s, 1C, 1×4° C.); 48.7 (s, 1C,1CH); 45.6 (s, 1C, 1CH); 37.1 (s, 1C, 1CH₂); 36.8 (s, 1C, 1CH₂); 28.7(s, 1C, 1CH₂); 24.7 (s, 1C, 1CH₂); ¹⁹F NMR (CDCl₃): δ-117.6 ppm. MS(ESI) (m/z, species, %): 206, [M+1], 10; 189, [M−16], 100.

Synthesis of(±)1-[2-(4-fluorophenyl)-bicyclo[2.2.1]hept-2-yl]-piperidine (Compound4; Table 1)

Anhydrous potassium carbonate (0.94 g, 6.8 mmol) and 1,5-dibromopentane(0.47 ml, 3.4 mmol) were added to a crude base of(±)2-(4-fluoro-phenyl)-bicyclo[2.2.1]hept-2-ylamine (compound 2;Table 1) (0.70 g, 3.4 mmol) in dry DMF (30 ml). The mixture was heatedto 50° C. and incubated for 8 hours. The mixture was then stirredovernight at room temperature and subsequently quenched with water. Theresultant mixture was extracted with chloroform (3×20 ml). Thechloroform extracts were combined and the chloroform was removed using arotary evaporator. The remaining residue was extracted with ether (2×25ml), and the ethereal extract was washed with water (2×20 ml) and driedover anhydrous sodium sulfate. A pale yellow oil was obtained afterremoving the ether. Purification by TLC with a mobile phase ofchloroform and diethyl ether (9:1) resulted in a colorless crystallinecompound (0.65 g, 70% yield, m.p. 58-59° C.).

The amine hydrochloride was synthesized by bubbling hydrogen chloridegas through the ethyl ether solution of(±)1-(2-(4-fluorophenyl)bicyclo[2.2.1]hept-2-yl)piperidine to givecolorless crystals (m.p. 86-88° C.). The solvent used forcrystallization was a mixture of methanol and ethyl ether.

The resultant free amine was characterized as follows by ¹H NMR (CDCl₃):δ 7.0-7.1 (m, 4H, 4 Ar—H); 1.0-2.3 (b, 20H, 9CH₂ and 2CH); ¹³C NMR(CDCl₃): δ 162.8 (s, 1C, 4′-C); 160.8 (s, 1C, 1′-C); 130.6 (s, 1C,5′-C); 130.5 (s, 1C, 3′-C); 113.8 (s, 1C, 6′-C); 113.6 (s, 1C, 2′-C);72.7 (s, 1C, 1×4° C.); 47.6 (s, 2C, 2CH₂); 41.9 (s, 1C, 1CH); 41.7 (s,1C, 1CH); 37.0 (s, 1C, 1CH₂); 35.2 (s, 1C, 1CH₂); 30.2 (s, 1C, 1CH₂);27.3 (s, 2C, 2CH₂); 24.7 (s, 1C, 1CH₂); 25.3 (s, 1C, 1CH₂); ¹⁹F NMR(CDCl₃): δ-118.4 ppm. MS (ESI) (m/z, species, %): 274, [M+1], 100.

Example 2 MES Test for Anti-Convulsive Activity

The maximal electroshock (MES) test was used to initially screencompounds for anti-convulsive activity in mice.

In the MES test, 50 mA of 60 MHz alternating current was delivered to19-25 g mice for 2 s by a corneal electrode which had been primed withan electrolyte solution containing an anesthetic agent (0.5% tetracaineHCl). Mice were tested at various intervals following doses of 30, 100or 300 mg/kg of test compound given by i.p. injection in 0.01 ml/g ofthe aqueous carrier. Animals are considered protected from MES-inducedseizures upon abolition of hindlimb tonic extensor component of theseizure (Swinyard et al. 1989; White et al. 1995a; White et al. 1995b).

Acute toxicity was assessed by monitoring animals for overt signs ofimpaired neurological or muscular function. The rotorod test measuresminimal motor impairment (MMI) by placing mice on a rod rotated a 6 rpm.A compound is considered toxic if the mice fall off the rod three timesduring a 1-min period. Additionally, mice were observed and noted forcircular or zigzag gaits, abnormal body posture and spread of the legs,tremors, hyperactivity, lack of exploratory behavior, somnolence,stupor, catalepsy, loss of placing response and change in muscle tone.

The results for the MES protection test and toxicity are shown in Table2. For activity, (+) means MES test protection occurred at 100 mg/kgdelivered i.p. in mice and (−) means that no activity was observed. Fortoxicity, (+++) means some animals died at 100 mg/kg and all animalsdied at 300 mg/kg; (++) means that some toxicity observed at 100 mg/kgand all animals died at 300 mg/kg; and (−) means no toxicity observed at100 mg/kg and some observed at 300 mg/kg but no animals died at 300mg/kg. TABLE 2 MES activity in Mice Cmpd. No. Cycloalkyl Phenyl AmineActivity Toxicity 2 bicyclo[2.2.1] 4-F amine + ++ 3 bicyclo[2.2.1] Hamine − +++ 4 bicyclo[2.2.1] 4-F piperidine + − bicyclo[2.2.1] H ether +++ cycloheptyl 4-F piperidine + +++ cycloheptyl 2-F amine + ++

The ether substituent in Table 2 is N-(—O—CH₂CH₂)piperidine. Based onthese results, it appears that a constrained or rigid alkyl ring, apara-substituted phenyl ring and piperidine are necessary for activityand reduced toxicity.

Compound 4 (Bicyclo,4-F-PCP) was tested in rats using 30 mg/kg deliveredorally. The ED₅₀ (effective dose) was determined to be 28.33 mg/kg whenadministered to rats by this route. Additionally, log P (i.e., a measureof lipophilicity) of bicyclo,4-F-PCP was determined to be 2.07, the pKa8.87 and the solubility of the fumarate salt thereof in aqueous solutionwas determined to be 0.0366 M or 14.2 mg/ml.

Example 3 MK-801 (Dizocilpine) Binding Site Assay

NMDA receptors were isolated from rat forebrain membrane (B_(max)=830fmol/mg protein) and incubated with ³H-labeled MK-801 maleate (15-30Ci/mmol) in 20 mM HEPES (pH 7.5) buffer at 25° C. for 90 min to yieldlabeled receptors. MK-801 is a known non-competitive antagonist of NMDAreceptor.

Selected concentrations of non-labeled bicyclo,4-F-PCP were incubatedwith the labeled receptors in 20 mM HEPES (pH 7.5) buffer at 25° C. for90 min. At the conclusion of the assay, the reaction mixture wasfiltered immediately on glass filters by vacuum filtration and washedtwice with buffer solutions. The radioactivity trapped on the filterswas measured, compared with controls, and the k_(i) and IC₅₀ values ofbicyclo,4-F-PCP were calculated.

As shown in FIG. 3, bicyclo,4-F-PCP can displace [³H] MK-801 maleatebound to NMDA receptors. This data demonstrates that bicyclo,4-F-PCP cancompete with MK-801 and bind inside of the NMDA receptor ion channel atnoncompetitive sites. This evidence reinforces the conclusion thatbicyclo,4-F-PCP and related compounds are noncompetitive NMDA receptorantagonists.

Example 4 NMDA Agonist Binding Site Assay

NMDA receptors were isolated from rat forebrain membrane (B_(max)=0.77pmol/mg tissue) and incubated with ³H-labeled CGP 39653 (15-30 Ci/mmol)in 50 mM TRIS-acetate (pH 7.4) buffer at 0-4° C. for 60 min to yieldlabeled receptors. CGP 39653 is a known competitive antagonist of NMDAreceptor.

Selected concentrations of non-labeled bicyclo,4-F-PCP were incubatedwith the labeled receptors in 50 mM TRIS-Acetate (pH 7.4) buffer at 0-4°C. for 60 min. At the conclusion of the assay, the reaction mixture wasimmediately filtered using glass filters and vacuum filtration, washingtwice with buffer solutions. The radioactivity trapped on the filterswas measured, compared with controls, and the k_(i) and IC₅₀ values ofbicyclo,4-F-PCP calculated.

As shown in FIG. 4, bicyclo,4-F-PCP does not displace the competitiveNMDA receptor agonist CGP 39653. This demonstrates that bicyclo,4-F-PCPdoes not compete with CGP 39653 (or with NMDA) at competitive sites onthe NMDA receptor. This evidence further reinforces the conclusion thatbicyclo,4-F-PCP and related compounds are noncompetitive NMDA receptorantagonists.

Example 5 scMET Test for Anti-Convulsive Activity

The subcutaneous metrozol seizure threshold test (scMET) can be used tomeasure anti-convulsive activity.

For scMET, mice are administered the test compound by i.p. injection ofdoses of 30, 100 or 300 mg/kg. Metrazol is injected into a loose fold ofskin in the midline of the neck at a dose to induce convulsions in 97%of the animals (85 mg/kg). Animals are placed in isolation in cages tominimize stress and observed for 30 min for the presence or absence of aseizure. An episode of clonic spasms, for approximately 3-5 seconds, ofthe forelimbs, hindlimbs, jaws or vibrassae is taken as the endpoint.Animals which do not meet this criterion are considered protected.

The disclosure of every patent, patent application, and publicationcited herein is hereby incorporated herein by reference in its entirety.

While this invention has been disclosed with reference to specificembodiments, it is apparent that other embodiments and variations ofthis invention can be devised by others skilled in the art withoutdeparting from the true spirit and scope of the invention. The appendedclaims include all such embodiments and equivalent variations.

1. A method of treating a subject afflicted with an ailment associatedwith over-activation of NMDA receptors on cells, the method comprisingadministering to the subject, for a time and in an amount sufficient toalleviate at least one symptom associated with the ailment, an NMDAreceptor antagonist having a chemical structure selected from the groupconsisting of Structures A, B, and C,

wherein R is selected from the group consisting of an electronwithdrawing group, a hydroxyl group, and an amino group, and wherein oneor more hydrogen atoms of the polycyclic ring of the antagonist areindependently optionally replaced with a lower alkyl group.
 2. Themethod of claim 1, wherein R is selected from the group consisting of afluorine atom, a chlorine atom, a bromine atom, an iodine atom, anitrate group, and a fluoromethyl group.
 3. The method of claim 1,wherein R is selected from the group consisting of a trifluoromethylgroup, a difluoromethyl group, and a monofluoromethyl group.
 4. Themethod of claim 1, wherein one or more hydrogen atoms of the polycyclicring of the antagonist is replaced with a lower alkyl group.
 5. Themethod of claim 1, wherein one or more hydrogen atoms of the polycyclicring of the antagonist are independently replaced with a moiety selectedfrom the group consisting of an ethyl group and a methyl group.
 6. Themethod of claim 1, wherein the antagonist has the chemical structure ofStructure A and wherein R is a fluorine atom.
 7. The method of claim 6,wherein none of the hydrogen atoms of the polycyclic ring of theantagonist is replaced.
 8. The method of claim 1, wherein the ailment isselected from the group consisting of cerebral ischemias, strokes,traumatic brain injuries, neuronal tumors, glutamate-dependent tumors,Alzheimer's disease, Parkinson's disease, epilepsy, schizophrenias,acute neuropathic pain, chronic neuropathic pain, sleep-relateddisorders, drug addictions, depression, vision-related disorders,ethanol withdrawal, anxiety, memory disorders, and learningdisabilities.
 9. The method of claim 1, wherein the ailment is epilepsy.10. The method of claim 1, wherein the ailment is a drug addiction. 11.The method of claim 10, wherein the drug is an opiate.
 12. The method ofclaim 11, wherein the ailment is neuropathic pain.
 13. The method ofclaim 1, wherein the ailment is a glutamate-dependent tumor.
 14. Themethod of claim 13, wherein the glutamate-dependent tumor is selectedfrom the group consisting of colon adenocarcinomas, breast tumors, lungtumors, and thyroid tumors.
 15. The method of claim 1, wherein theailment is a neurodegenerative disorder.
 16. The method of claim 15,wherein the disorder is selected from the group consisting ofAlzheimer's disease and Parkinson's disease.
 17. The method of claim 1,wherein the antagonist is administered to the subject in the form of apharmaceutically acceptable salt.
 18. The method of claim 1, wherein theantagonist is administered to the subject as a pharmaceuticalcomposition comprising the antagonist and a pharmaceutically acceptablecarrier.
 19. The method of claim 1, wherein the subject is a human. 20.The method of claim 1, wherein the cells are neuronal cells.
 21. Themethod of claim 1, wherein the cells are selected from the groupconsisting of brain cells and cells of the spinal cord.
 22. A method ofalleviating in a subject at least one symptom associated withover-activation of NMDA receptors on cells, the method comprisingadministering to the subject, for a time and in an amount sufficient toalleviate the symptom, an NMDA receptor antagonist having a chemicalstructure selected from the group consisting of Structures A, B, and C,

wherein R is selected from the group consisting of an electronwithdrawing group, a hydroxyl group, and an amino group, and wherein oneor more hydrogen atoms of the polycyclic ring of the antagonist areindependently optionally replaced with a lower alkyl group. 23-28.(canceled)
 29. An NMDA receptor antagonist having a chemical structureselected from the group consisting of Structures A, B, and C,

wherein R is selected from the group consisting of an electronwithdrawing group, a hydroxyl group, and an amino group, and wherein oneor more hydrogen atoms of the polycyclic ring of the antagonist areindependently optionally replaced with a lower alkyl group. 30-35.(canceled)